As the geometric and positional isomers of elongated unsaturated fatty acids have been shown to change the function and the architecture of the macromolecules into which they are incorporated, it seems desirable to study the relationship between their function andstructure in two simultaneous studies. In one study, the rate of oxygen consumption of heart mitochondria in the presence or absence of ADP will be measured polarographically by means of a Clark oxygen electrode in order to determine whether the incorporation of elongated polyunsaturated fatty acids into heart mitochondria influences their metabolic activity. The mitochondria will be obtained from the hearts of rats which had been fed commercial fats containing trans fatty acids or synthetically prepared H3 or C14 labeled PUFA isomers incorporated into trans free dietary fat. The labeled PUFA isomers will be prepared by coupling 1, 2 H3 trans-1-bromo-1-aakene with 1-C14 w bromoalkanoic acid. In the other study, the relationship between phosphoglycerides (structure) and the functional properties of the endoplasmic reticulum will be determined. Rat livers from animals maintained on fat deficient, corn oil or partially hydrogenated soybean oil diets will be used. The livers will be used. The livers will be homogenized in 0.25 M glucose, centrifuged and the final microsomal suspension frozen until ready for use. Glucose-6-phosphatase and acyl CoA synthetase activity will be assayed and the results correlated with the total and the individually characterized phospholipids in the microsomal fraction. The use of heart mitochondria and the liver microsomal fraction from rats fed various geometric and positional isomers of unsaturated fatty acids as a model system, may provide the background data that seems necessary to an understinging of the functional role of the PUFA in heart mitochondria and of the role of the phosphoglycerides in membranes and in possible processes that result in lipid infiltration of the smooth muscle cells in the arterial mesenchyme.